Cut and pasted from a previous thread: (You will need to read, and copy the part numbers)
Do you know when to service your CDR valve?

All 6.9L and 7.3L diesel engines are equipped with a CDR (Crankcase Depression Regulator) valve. Even the new 7.3L Power Stroke is also equipped with the same valve. The CDR valve is one of the leading causes of head gasket failure in these engines. The CDR valve is responsible for controlling the pressure/vacuum in the engine crankcase, and seperating the oil mist from the air and returning the oil to the crankcase. The CDR valve should be serviced every second oil change or when signs listed below are seen.

When the CDR valve is not properly serviced, engine oil enters the air intake and is drawn into the engine. The diesel engine will burn this oil as fuel, however, it is heavier and thicker than diesel fuel and, having greater BTU output, causes excessive heat in the cylinder. Due to the intake manifold design, most of the oil will migrate to #7 and #8 cylinders; the last two cylinders in the rear by the firewall. The increased temperature here will cause the cylinder head to lift off the gasket and allow water or oil to leak out the back of the cylinder head where it meets the block.

To check your CDR valve, remove the air cleaner hold down bolt and inspect it. If the bolt is covered with engine oil mist, it's time to service your CDR valve! Ford calls this item a "Adapter assembly for Crankcase Ventilation" Part number E3TZ-6A665-A or IH part #1805319C1


To service the CDR wash with a solvent, allow to dry, do not use compressed air to dry. There is a small hole in the CDR back cover, ensure it is clean and open. If black chunks of rubber are visible in the intake, on the screen then the rubber membrane has disintegrated, replace the CDR.